Accepted Manuscript Characteristics and significance of the penecontemporaneous karst in lacustrine carbonate, Da'anzhai member, lower Jurassic, Beibei area, eastern Sichuan basin Chengpeng Su, Xiucheng Tan, Kailan Shi, Juan Zou, Feifan Lu, Sicong Luo, Hao Tang, Xinyu Zhang PII: S2405-6561(16)30214-0 DOI: 10.1016/j.petlm.2016.12.006 Reference: PETLM 130 To appear in: Petroleum Received Date: 26 October 2016 Revised Date: 15 December 2016 Accepted Date: 29 December 2016 Please cite this article as: C. Su, X. Tan, K. Shi, J. Zou, F. Lu, S. Luo, H. Tang, X. Zhang, Characteristics and significance of the penecontemporaneous karst in lacustrine carbonate, Da'anzhai member, lower Jurassic, Beibei area, eastern Sichuan basin, Petroleum (2017), doi: 10.1016/ j.petlm.2016.12.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. 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ACCEPTED MANUSCRIPT Characteristics and significance of the penecontemporaneous karst in lacustrine carbonate, Da ′anzhai Member, Lower Jurassic, Beibei area, Eastern Sichuan Basin Chengpeng Su a,c, Xiucheng Tan a,b, *, Kailan Shi c, Juan Zou d, Feifan Lu c, Sicong Luo c, Hao Tang a,b, Xinyu Zhang c a State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, 610500, China b The sedimentary and accumulation department of key laboratory of carbonate reservoirs, PetroChina, Southwest Petroleum University, Chengdu, 610500, China c School of Geoscience and Technology, Southwest Petroleum University, Chengdu, 610500, China d Exploration and Development Research Institute of PetroChina Southwest Oil & Gas Field Company, Chengdu, Sichuan 610041, China Abstract ：There are few reports about the penecontemporaneous karst of the lacustrine carbonate of Da ′anzhai Member which developed on the top of Lower Jurassic Ziliujing Formation, eastern Sichuan Basin. Based on the analysis of the macroscopic and microscopic characteristics of Heping Reservoir section in Beibei area, It is discovered that the penecontemporaneous karst in the lacustrine carbonate, Da ′anzhai Member, and its characters as follows: (1) The dissolved fracture and karren are common, which have been filled with vadose silts, bioclasts, terrigenous quartzes, crystal and intergrown calcites; (2) The penecontemporaneous karstification mainly occurs in the micrites and shell limestones of the middle and upper part of the shallowing-upward sequence, and the desiccation cracks occur in some shallowing-upward sequences; (3) Three meteoric-water diagenetic lenses are identified in this section. By further study we also find the factures, stylolite and burial dissolution pores occur along the karst system (tubes, conduits and caves of the karst). And the asphalt not only fills the stylolites and fractures, but also is mixed with the vadose silt in the karst system, although the pore space formed by penecontemporaneous karstification is filled with vadose material and cements. Therefore it is concluded that the development and modification of the tight lacustrine carbonate reservoir of Da ′anzhai Member, to some extent, are relevant with the penecontemporaneous karstification, and the penecontemporaneous karst reservoir may develop in the buried Da ′anzhai carbonate of the basin. Key words ：Sichuan Basin; Da ′anzhai Member; lacustrine carbonate; penecontemporaneous karst; tight reservoir 1 Introduction The tight lacustrine carbonate reservoir of Da ′anzhai Member, Ziliujing Formation in Lower Jurassic is one of the main producing pays in Sichuan Basin [1-3]. AccordingMANUSCRIPT to former studies, the reservoir is controlled by sedimentary facies and mainly formed in the high-energy shell (bioclastic) beach developed area. The major of rock types are bioclastic limestone, shell limestone and mud-bearing shell limestone. Meanwhile, the reservoir space type is pore-fracture pattern, and fractures are the prime reservoir space and vadose channel [4-8]. There is a popular belief that the primary porosity of Da ′anzhai Member’s limestone is barely vanished due to the intense compaction and cementation during inchoate diagenesis. But fractures formed by later-structural rupture and moniliform corrosion pores formed by the corrosion along fractures improve the property of reservoir in rocks tremendously [4-5, 9]. The corroded pores are formed by organic material dissolved acid waters or compacted water in shale during burial period generally [6, 10]. Zheng et al. [10] once briefly introduced the sources of different stages’ corroded hydrothermal fluid in Da′anzhai Member, north Sichuan. The limestone of regionally successively-sedimentary Da ′anzhai part has some sedimentary hiatus in some area, according to research of first sub-member of Da′anzhai in south Langzhong area made by Liu at al. [11]. Meanwhile, the limestone are cropped out and early pores and holes are formed by the corrosion of surface water. They thought that the leading cause of the reservoir formation in the first sub-member of Da ′anzhai is the shallow water of later sedimentation, which result in the effortlessACCEPTED exposure to the surface and corrosion [11-12]. Nevertheless, this viewpoint does not get much attention in recent ten years and merely several authors mention it without deeper research [13-14]. In view of this, the paper set the Da ′anzhai member of Heping Reservoir outcrop in Beibei area, east Sichuan as an example. Based on the macroscopic and microscopic characteristics, the paper studies the identification mark of penecontemporaneous karstification and its impact on the reservoir. Moreover, the paper provides referential * Corresponding author. #8 Xindu Road, Xindu District, Chengdu, 610500, China. E-mail address : [email protected] （C. Su ）, [email protected] (X. Tan) ACCEPTED MANUSCRIPT information to the exploration of tight oil reservoir of lacustrine-carbonate in Da ′anzhai member. 2 Geological Background The Long’men Mountain in west Sichuan keeps rising due to the influence of later Indosinian Movement, vast regions of Sichuan Basin turn into inland lake basin. The Xujiahe Formation of upper Triassic, Ziliujing Formation, Shaximiao Formation, Suining Formation and Penglaizhen Formation of Jurassic are deposited in the basin from the bottom up. Meanwhile, the area of lake surface in Da ′anzhai member, Ziliujing Formation, lower Jurassic is the widest among them. The area of the lake surface is more than 10×10 4 square kilometers and the asymmetric vast lake basin is steep in the north and gently in the south [15-16]. Furthermore, Da ′anzhai deposit period has an integrated cycle: lake transgression, maximum lake transgression and lake regression. The third sub-member of Da ′anzhai is corresponding to the initial stage of lake transgression and the main lithology is shell limestone (bioclastic limestone) mixed with some shale. The second sub-member of Da ′anzhai corresponds to the deepwater stage of maximum lake transgression; sediments are mainly dark-color shale mix with some micrites and little shell limestone. Meanwhile, the first sub-member of Da ′anzhai corresponding to the lake regression stage is the main reservoir-developing Formation for Da ′anzhai [17-19], which generate abundant shell limestone (bioclastic limestone) mixed with a little dark shale. On the plane (Fig. 1), the depocenter of lake basin during Da ′anzhai stage, locates over Yilong and Yinshan. Semi-deep lake, shallow lake to semi-deep lake, shore-shallow lake, shore lake and river facies are developed from the center to circum [20-21]. The shell beach (bioclastic beach) is primarily composed by shell limestone (bioclastic limestone), which is intensely distributed in upper slopes of shallow lake, shore-shallow lake outward-surrounded the depocenter [22-23]. MANUSCRIPT Fig.1. Geographical location map of study section and palaeogeogrphy of Da’anzhai Member, lower Jurassic in Sichuan Basin (modified from Zheng et al., 1997) The research sectionACCEPTED is belonging to high fold belt of eastern Sichuan basin, which locates in the Heping reservoir, Dabagou, Tianfu town, Beibei area, Chongqing (Fig. 1). Structure activity of eastern Sichuan basin and Sichuan basin’s periphery are relatively stable in Da ′anzhai stage, and there are no obvious lifting and settling [12, 17]. Furthermore, Shaximiao Formation, Suining Formation and Penglaizhen Formation are all conformable contact in Beibei area. Eastern Sichuan basin area experiences intense folding due to the effect of Yanshan Movement and Himalayan Movement, which generate nowadays high fold belt in eastern Sichuan basin after the extruding lifting and transformation of the Jurassic and strata under it [24]. The research area locates in shore-shallow lake facies of south lake basin. Rock types are multiple, which are ACCEPTED MANUSCRIPT mainly amaranthine calcareous mudstone in shore lake and dark-gray micrite in shallow lake. Meanwhile, shell limestone and bioclastic limestone which constitute shell beach and bioclastic beach are partly developed and the thickness of one single layer is less than 1.5 meter. Besides, micritic dolomite with exposed mark (mudcrack or penecontemporaneous